Fuse link



Feb. 25, 1947. BOOTHE 2,416,428

FUSE LINK Filed June 22, 1945 INVENTIOR EUGENE F. BOOTHE BY W,

ATTORNEY Patented Feb. 25, 1947 FUSE LINK Eugene F. Boothe, St. Louis, .Mo., assignor to James R. Kearney Corporation, St. Louis, Mo., a corporation of Missouri Application June 22, 1945, Serial No. 691,000

9 .Claims.

Thi invention relates generally to fuse links of the type adapted for employment in association with electrical protective devices, such as fuse switches and cutouts, and more specifically to such fuse links which are rupturable in service by passage therethrough of abnormal current, and which may be replaced in service by intact fuse links when so ruptured, the predominant object of the invention being to provide such a fuse .link which is of such improved construction and arrangement that it possesses certain desirable rupturing characteristics, and, also, is of the required tensile strength to enable the fuse link to perform its intended function in a highly eflicient manner.

Some years prior to this invention a'fuse link structure was devised which included an element wire and a strain wire that were attached to suitable terminals. This fuse link construction gave a fairly steep time-current curve which was found to be objectionable in some instances, in that a fuse link which would operate as desired on a high value of fault current would not provide sufficient protection at low values of fault current.

Subsequently, in an endeavor to provide a fuse link construction which would give a more gradual slope in the long time range, a fuse link construction was developed which consisted of two element members that were lapped and soldered at their point of lapping relation. On high values of fault current, in the use of this type of fuse link, melting would take place at a single thickness element section, and apart from the lapped section of the element members, thus giving substantially the same steep time-current curve obtained in the use of the earlier fuse link construction referred to immediately above. On lower values of fault current, the soldered joint of the lapped type of fuse link construction would melt, thereby giving a time-current curve which was somewhat better for certain applications, but the tensile'strength of this construction was found to be insufficient for service requirements, inasmuch as the soldered joint would, in many cases, gradually pull apart, when subjected tonormal service tension, and the fuse link would open even though the current passing therethrough had not been above normal value.

The fuse link structure of the present invention is of vsuch improvedand .unique construction and arrangement that the objections recited above as being present'ln connection with the use :of earlier fuselink structurestare eliminated, said improved fuse link structure of the present.

invention providing the desired slow sloping time-current curve, and at the same time being possessed of the necessary high tensile strength to permit the improved fuse link structure to perform its intended function in a highly efficient manner.

Fig. 1 is a view partly in elevation and partly in longitudinal section illustrating the improved fuse link structure.

Fig. 2 is a cross-section taken on line 22 of Fig. .1.

Fig. .3 is a cross-section taken on line 3-3 of Fi 1.

Fig. 4 .is a view, partly in vertical section and partly in elevation, which illustrates a modified form of the invention.

In the drawing, wherein is shown for the purpose of illustration, merely, one embodiment of the invention, -A designates in Fig. 1 the improved fuse link generally. The fuse link A is provided at one of its ends, the upper end as the fuse link is illustrated in Fig. 1, with a terminal member 1. The terminal member I is provided with a substantially circular portion 2 having a circumferential face which is milled, orotherwise roughened, there being a neck portion 3, of slightly reduced diameter, extending upwardly from said portion 2 which integrally joins said portion 2 and a flange portion 4 of increased diameter. The flange portion 4 has extended upwardly therefrom a screwthreaded shank portion 5 on which is mounted a terminal button =6, said terminal button being provided with a screwthreaded opening in which the screwthreaded shank 5 of the terminal member I is screwthreadedly received so that the lower face of the terminal button abuts against the upper face of the flange portion 4 of said terminal member I. The terminal member I includes, also, a hollow, lower portion 1 which is integrally joined to the circular portion 2 of said terminal member by a neck portion 8.

Secured to the terminal member I is strain wire 9 which is formed of material that is of high tensile strength and low electrical conductivity, the upper end portion of said strain wire 9 being inserted into the hollow portion 1 of the terminal member I and said hollow portion 7 being subjected to a swaging operation so as to cause said-strain wire to be securely gripped by said Jhollow portion 1 of the terminal member I. The opposite endportion of the strain wire 9 is introduced into a lower terminal member H] which iforms a part of the fuse link structure. this lower "terminal member l0 being hollow so 3 as to receive said end portion of the strain wire and the strain wire being securely fixed to the lower terminal member by subjecting said lower terminal member to a swaging operation.

The improved fuse link A includes a pair of electrical conductive elements II and I2 which are formed of material characterized by being of high electrical onductivity and relatively low tensile strength. The element II has an end portion thereof extended into the hollow portion I of the terminal member I, and this end portion of said element II is securely gripped by said hollow portion because of the swaging operation to which said hollow portion is subjected. Likewise, the conductive element I2 has an end thereof extended into the hollow, lower terminal member I0, and this extended end portion of said conductive element I2 is secured to said lower terminal member I by the swaging operation to which it is subjected.

As is shown in Fig. l, the inner, adjacent ends of the conductive elements II and I2 are spaced apart a considerable distance, and said conductive elements I I and I2 are electrically joined by a spirally extended conductive element I3 which is formed of material characterized in a cordance with the material from which the conductive elements I I and I2 are formed. The intermediate portion of the spirally extended conductive element I3 embraces the strain wire I 9 and the opposite end portions of said spirally extended conductive element respectively embrace the strain wire 9 and end portions of the conductive elements II and I2. Preferably, the opposite end portions of the spirally extended conductive element I3 are more closely coiled than is the intermediate portion of said spirally extended conductive element, the closely coiled portion at one end of the spirally extended conductive element I 3 being secured by suitable solder to the conductive element II, while the closely coiled portion at the opposite end of said spirally extended conductive element I3 is secured by suitable solder to the conductive element I2. It will be noted by reference to Fig. 1 that the lower terminal member ID has secured thereto a flexible conductor I4, an end portion of said flexible conductor being extended into said lower terminal member and being gripped thereby by a swaging operation to which said lower terminal member is subjected.

Arranged in embra ing relation with respect to portions of the strain wire 9 and the conductive element I I is a short tube I5 which is formed of fiber, or other suitable electrical insulating material, said tube abutting at one of its ends against the closely coiled end portion of the spirally extended conductive element I3 which is soldered to said conductive element II. Interposed between the opposite end of the tube I5 and the lower face of the portion 1 of the terminal member I, is a coil spring I6, said coil spring being under compression between said tube I 5 and said portion 7 of the terminal member I so that it tends to move said tube downwardly. The improved fuse link structure includes, also, an outer tubular member I1, formed of suitable insulating material, which embraces the conductive elements II and I2 and the strain wire 9, together with adjacently located parts of the fuse link structure, the upper end of said tubular member. abutting against the lower face of the flange portion 4 of the terminal member I, and said tubular member being frictionally gripped by the milled circumferential face of the portion 2 0f 4 said terminal member I so that it is held in place.

When tension is applied to the improved fuse link disclosed herein, when same is in service, the line of tension is through the button 6, the terminal member I, the strain wire 9, the lower terminal member ID, and the conductor I4. Thus the conductive elements I I, I2, and I3, and the soldered joints which connect said conductive elements are relieved of all tension to which the fuse link is subjected because of its use in service. The normal electrical path through the fuse link is through the button 6, the terminal member I, the conductive elements II, I3, and I2, the lower terminal member ID, and the conductor I l. The strain wire 9 is in parallel with the'conductive elements II, I3, and I2, but the conductivity ratio is such that but little current flows through said strain wire as long as the conductive elements II, I2, and I3 are intact and are electrically connected.

The flow of current through the conductive elements II, I2, and I3 tends to heat the soldered joints which connect said conductive elements together, and when the current reaches a predetermined value, said soldered joints melt. When this occurs the force of the coil spring I6 moves the tube I5 downwardly so as to strip the upper end portion of the spirally arranged conductive element It from the lower end portion of the conductive element I I, the force of said coil spring moving the spirally arranged conductive element I3 bodily, longitudinally of the strain wire 9 so as to provide a substantial-gap between the upperend of the spirally arranged conductive element I3 and the conductive element II, and the lower portion of said spirally arranged conductive element I3 moving downwardly with respect to the conductive element I2. Thus the normal conductive electrical path through the fuse link is broken, and all of the current then flows through the strain wire which melts immediately, and passage of current through the fuse link is completely interrupted. When, in the use of the improved fuse link, the fault current exceeds a higher predetermined value, one of the conduc tive elements II, I2, or I3, will melt before the soldered joints have time to melt and separate and when this happens the current path is transferred to the strain wire which immediately melts to interrupt passage of current through the fuse link.

The force which the coil spring I6 exerts, through the tube I5, against the soldered joint which joins the conductive elements II and I3 is sufficient to separate said conductive elements I I and I3 only after the soldered joints which join the conductive elements II, I2, and I3, have melted; that is to say, said force of the coil spring is low relative to the strength of the soldered joints at normal load temperatures. The soldered joints which join the conductive elements II, I2, and I3 are thus subjected only to a safe, low con stant force, and mechanical failure which might otherwise result from external tension applied to the fuse link in use, is eliminated. Animportant consideration in this connection is that external tensions to which fuse links are subjected in service vary between rather wide limits, and this variation caused fuse links of the types heretofore employed to, vary between correspondingly wide time-current limits. In the case of the fuse link of the present invention, however, "the improved method of'relieving the soldered joints from external'tension curve accuracy.

gives greater time-current Still another important 1' advantage re'alized'in theiuse'of the improved 'fuselinktstructure disclosed herein is that the spiral formation ofthe conductive element l3 increases the concentration of 'heat at points closely adjacent'to the .soldered joints. The result is that a slower .or more gradually sloping time-current curve is ob tained. in the use of the improved fuse link. Thus, theimproved construction of theiuse link disclosed herein renders it possible to obtain amorc gradual-time-current slope with a given type of solder at the soldered joints, while a higher temperature solder may be employed 'at the soldered joints to obtain a different degree :of time-current curve slope.

Fig.4 illustrates a modified form of the invention illustrated by Figs. 1, 2, and 3;of the draw ing. The structure of Fig. 4 comprises an'upper terminal portion 1a and a. lower terminal [a between which is extendecla strain wire 9a, the upper terminal portion la and the lower terminal 10a being hollow and respectively receiving therein the opposite end portions of the'strain wire 9a which are caused to be gripped by said upper terminal portion and said lower terminal because of 'swaging operations to'which said upper terminal portion la and said 'lowerterminal Illa are subjected.

Gripped by the swaged upper terminalportion I a is the unper end portion of a conductive element l8, said conductive element 18, below the gripped, upper end portion thereof, being ofspiral formation. and said spiral portion of said conductive element being arranged in embracing relat on with respect to the stra n wire a. Likewise. the structure of F g. 4 includes a lower conductive element I9, which is similar to the conductive element !8, said conductive element 19 having its lower end portion gr pped by the swaged. lower terminal Ilia and being provided w th a. spiral portion that embraces the strain wire 9a. The lower portion of the spiral part of the conductive element l8 and the upperportion of the spiral p rt of the conductive element l9 are relatively closely co led. "and said i closelv co led portions are spaced apart a substantial distance to provide aptherebetween. Ex ended across the gap between the closely coiled end p"r i0ns of the spral conductive elements !8 and I9 is a substan ially strai ht conductive element 20, the upper end portion of said conductive element 20 being secured by su able solder to the closely coiled lower end portion of the conductive element l8, and the lower end portion of sa d conductive element 2L be ng secured by suitable solder to the closely coiled upper portion of the conductive element 19.

Arranged in embracin relation with respect to adjacent por ions of t e str in w re 9a and t e co duct ve element 23 is a tube 2| wh chis formed of fiber. or other suitable e ectrical insulating material. the upper end of "said tube being arranged in abutting relation with respectto 'lower end of the lower, close v coiled portion of the conductive element [8. The conductive element 28 has so dered, or ot erwise secured thereto. an abutment element 22. and in erposed between said abutment and'said tube, with its opposite e ds in contact w th'said parts. is a coile'd'spring 23. The coil spring 23 is under compression so that it tends to move the tube '21 and the abutmentelement'fl away from each other.

The flow of current through "the conductive elements 18, i9, and Y20 tends to heat the soldered joints which connect saidconductive elements together, and when the current reaches a predetermined value, :said soldered joints melt. When this "occursthe force of the coil spring 23 moves the conductive element '29 downwardly, longitudinally'of'thestrain wire 91:. so as to provide 'a substantial gap between the upper end portion of saidconductive element 20, and the lower portion of the conductive element It. Thus, the normal conductive path through the fuse link'is broken and all of the current then flows through the strain wire 9a which melts immediatelmand passage :of current through the fuse .link is completely interrupted.

I claim:

1. .A fuse'link comprising a pair of spaced terminal members, 'astrain element secured atits opposite ends to said terminal members and eX- tended therebetween, means providing an'electrical conductive'path from one to the other of said terminal members, said 'means including an electrical conductive element, a second electrical conductive element associated with the firstmentioned electrical conductive element, and meltable means for securing said second electrical conductive element to the first-mentioned electrical conductive element, and means formirrg part of the fuse link operable on melting of'said meltable meansto separate said second electrical conductive element "from the firstmentioned electrical conductive element to interrupt the electrical conductive path normally provided "thereby, the last-mentioned means comprising a member which embraces one of said elec rical conductive elements and engages a portion of the other of said electrical conductive 'elernents,.and spring means for moving said member so as to effect separation of said second electrical conductive element from said firstmentior'ed electrical conductive element.

'2. A fuse'link comprising pair of spaced terminal members, "a strain element secured at its oppo i e end itosa d terminal members and extended therebetween, means providing an electrical conductive'path from one to the other of said terminal members. said means includin an electrical conductive element. a second electrical conductive element associated with the firstmentioned electrical conductive element. and meltable means for securing said second electrical 'conductiveelement to the first-mentioned electrical conductive element. and means operab e on melting of said meltable means to separate said second elec rical conductive element from the first mentioned electrical conductive element to interrupt the electrical conductive path'normally provided'thereby. the last-mentioned "means comprising a tubular member which embraces said first-mentioned electrical conductive element and said strain element and which e gages aportion of saidsecond electrical conductive element, and spring means for moving said tubular member so as to effect separation o'i said second electrical conductive element from said first-mentioned electrical conductive element.

3. A fuse l nk compri ing a pa r of spaced terminalmembers, a strain element secured at its opposite ends to said terminal members extended therebetween. means providing an electrical conductivepath from one to the other of said terminal members. saidmeans'includ ng an electrical conductive element, a'second electr cal conductive element associated with the firstmentioned electrical conductive element, and meltable means for securing said second electrical conductive element to the first-mentioned electrical conductive element, and means operable on melting of said meltable means to separate said second electrical conductive element from the first-mentioned electrical conductive element to interrupt the electrical conductive path normally provided thereby, the last-mentioned means comprising a tubular member which embraces said first-mentioned electrical conductive element and said strain element and which engages a portion of said second electrical conductive element, and spring means interposed between said tubular member and one of said pair of spaced terminal members for moving said tubular member so as to efiect separation of said second electrical conductive element from said first-mentioned electrical conductive element.

4. A fuse link comprising a pair of spaced terminal members, a strain element secured at its opposite ends to said terminal members and extended therebetween, means providing an electrical conductive path from one to the other of said terminal members, said means comprising a pair of electrical conductive elements having adjacent inner ends which are spaced apart to provide a gap therebetween and which are secured respectively at their outer ends to the respective terminal members, a third electrical conductive element which extends across said gap from one to the other of said pair of electrical conductive elements, and meltable means for securing an nd portion of said third electrical conductive element to one of said pair of electrical conductive elements, and means forming part of the fuse link operable on melting of said meltable means to separate said third electrical conductive element from the electrical conductive element to which it is normally secured by said meltable means to interrupt the electrical conductive path through the fuse link, the last-mentioned means comprising a member which embraces one of said electrical conductive elements and engages a portion of another of said electrical conductive elements, and spring means for moving said memher so as to effect separation of said third electrical conductive element from the electrical conductive element to which it is normally secured.

5. A fuse link comprising a pair of spaced terminal members, a strain element secured at its opposite ends to said terminal members and extended therebetween, means providing an electrical conductive path from one to the other" of said terminal members, said means comprising a pair of electrical conductive elements having adjacent inner ends which are spaced apart to provide a gap therebetween and which are secured respectively at their outer ends to the respective terminal members, a third electrical conductive element which extends across said gap from one to the other of said pair of electrical conductive elements, and meltable means for se curing an end portion of said third electrical conductive element to one of said pair of electrical conductive elements, and means operable on melting f said meltable means to separate said third electrical conductive element from the electrical conductive element to which it is normally secured by said meltable means to interrupt the electrical conductive path through the fuse link, the last-mentioned means comprising a tubular member which embraces one of said pair of electrical conductive elements and'sald strain element and which engages a portion of said third electrical conductive element, and spring means for moving said tubular member so as to effect separation of said third electrical conductive element from the conductive element to which it is normally secured.

'6. A fuse link comprising a pair of spaced terminal members, a strain element secured at its opposite ends to said terminal members and extended therebetwcen, means providing an electrical conductive path from one to the other of said terminal members, said means comprising a pair. of electrical conductive elements having adjacent inner ends which are spaced apart to provide a gap therebetween and which are secured respectively at their outer ends to the respective terminal members, a third electrical conductive element which extends across said gap from one to the other of said pair of electrical conductive elements, and meltable means for securing an end portion of said third electrical conductive element to one of said pair of electrical conductive elements, and means operable on melt ing of said meltable means to separate said third electrical conductive element from the electrical conductive element to which it is normally secured by said meltable means to interrupt the electrical conductive path through the fuse link, the last-mentioned means comprising a tubular member which embraces one of said pair of electrical conductive elements and said strain element and which engages a portion of said third electrical conductive element, and spring means interposed between said tubular member and one of said pair of spaced terminal members for moving said tubular member so as to effect separation of said third electrical conductive element from the conductive element to which it is normally secured;

7. A fuse link comprising a pair of spaced terminal members, a strain element secured at its opposite ends to said terminal members and extended therebetween, means providing an electrical conductive path from one to the other of said terminal members, said means comprising a pair of electrical conductive elements having adjacent inner ends which are spaced apart to provide a gap therebetween and which are secured respectively at their outer ends to the respective terminal members, a third electrical conductive element which extends across said gap from one to the other of said pair of electrical conductive elements, and meltable joints for securing the opposite end portions of said third electrical conductive element to the respective electrical conductive elements of said pair of electrical conductive elements, and means operable on melting of said meltable joints to separate an end portion of said third electrical conductive element from one of said pair of electrical conductive elements to which said end portion of said third electrical conductive element is normally secured by one of said meltable joints, thelast-mentioned means comprising a tubular member which embraces one of said pair of electrical conductive elements and said strain element and which engages the separable end portion of said third electrical conductive element, and spring means for moving said tubular member so as to effect separation of said end portion of said third electrical conductive element from the electrical conductive element to which it is normally secured.

8. -A fuse link comprising a pair of spaced terminal members, a strain element secured at its opposite ends to said terminal members and extended therebetween, means providing an electrical conductive path from one to the other of said terminal members, said means comprising a pair of electrical conductive elements having adjacent inner ends which are spaced apart to provide a gap therebetween and which are secured respectively at their outer ends to the respective terminal members, a third electrical conductive element which extends across said gap from one to the other of said pair of electrical conductive elements, and meltable joints for securing the opposite end portions of said third electrical conductive element to the respective electrical conductive elements of said pair of electrical conductive elements, and means operable on melting of said meltable joints to separate an end portion of said third electrical conductive element from one of said pair of electrical conductive elements to which said end portion of said third electrical conductive element is normally secured by one of said meltable joints, the lastrnentioned means comprising a tubular member which embraces one of said pair of electrical conductive elements and said strain element and which engages the separable end portion of said third electrical conductive element, and spring means interposed between said tubular member and one of said pair of terminal members for moving said tubular member so as to efiect separation of said end portion of said third electrical conductive element from the electrical conductive element to which it is normally secured.

9. A fuse link comprising a pair of spaced terminal members, a strain element secured at its opposite ends to said terminal members and extended therebetween, means providing an elec- 10 trical conductive path from one to the other of said terminal members, said means comprising a pair or electrical conductive elements having adjacent inner ends which are spaced apart to provide a gap therebetween and which are secured respectively at their outer ends to the respective terminal members, a third electrical conductive element which extends across said gap from one to the other of said pair of electrical conductive elements and which is arranged spirally about said strain element and meltable joints for securing the opposite end portions of said third electrical conductive element to the respective electrical conductive elements of said or electrical conductive elements, and means operable 0n melting of said meltable joints to separate an end portion of said third electrical conductive element from one of said pair of electrical conductive elements to which said end portion of said third electrical conductive element is normally secured by one of said meltable joints.

EUGENE F. BOOTHE.

REFERENCES CITED The ioiiowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,998,042 Boothe Apr. 16, 1935 2,333,345 Steinmayer Nov. 2, 1943 2,089,172 Boothe Aug. 10, 1937 1,595,742 Taylor Aug. 10, 1926 2,093,509 Boothe Sept. 21, 1937 2,256,360 Steimnayer et al. Sept. 16, 1941 2,090,609 Lemmon Aug. 1'7, 193'? 2,326,031 Hodnette et a1 Aug. 3, 1943 

